F20A 's resistors*' location ( below bonnet, too hot ) is very wrong.
* own heat when input voltage is 13.5 v is already 13.5²/ 9.2 ( 7 + 2.2 ohm ) = 19.8 watt ( assuming 4 injectors in total receive current all the time ), hit by hot air from 2 radiators, so * are hot : *'s heat flow toward injectors, so injectors are too hot for nozzles to be clean.
In 2-10 I used a 3½ amp buck convertor, 1 diode, 5 capacitors ( 0.15 F ) & 1 inductor ( 94 mH ) to feed 4.5 v to injectors : wax clogging nozzles came loose 1 by 1, each time I could feel a small ↑ in torque.
This mth I put * ( with 5 extn wires ) in the space under wiper arm, tape a aluminium dish onto *'s ceramic, file & flatten *'s hsink fins by ½ mm, rub silicone on fins, fit a big 2ndary hsink, put a polystyrene tray underneath, * & wires then much cooler. Idle rpm ↑300, torque ↑15%, coolant's heat ↓10%.